In U.S. Pat. No. 3,168,656 to Kobbe there is described a delay line of substantially uniform characteristic impedance having its input end terminated in an impedance substantially equal to the characteristic impedance of the line. At the output end of the line a resistor and the emitter junction of an amplifying transistor are connected in series to form the terminating impedance which is connected to ground at the base of the transistor. The sum of the resistances of the resistor and the emitter junction is made substantially equal to the characteristic impedance of the line. The transistor is connected as a common base amplifier so that current flowing through the emitter junction provides a voltage output at the collector of the transistor. By employing this current-actuated amplifying transistor as part of the output end termination impedance the gain of the transistor compensates for any loss of signal energy due to termination of the output line in its characteristic impedance.
While the above discussed circuit terminates the line in its characteristic impedance to minimize spurious signals due to reflection of signal energy in the delay line, and compensates for any loss of signal energy due to termination of the output in its characteristic impedance, the circuit cannot be used where the terminating impedance must be high and the reflection coefficient must be unity. These requirements occur in applications implemented with a single delay line providing special transient effects of a single terminated delay line such as correcting distortion of a television signal due to the size of the electron beam by boosting the high frequency gain in a phase linear manner. This application requires a symmetrical preshoot and aftershoot over the range of the correction which is not possible utilizing the Kobbe teachings.
In "Wave Generation And Shaping" by Leonard Strauss (pages 464-516) there is described how positive-current feedback can be used with an ideal current amplifier to produce a negative input impedance; if current amplification within the active region is positive or greater than unity, the input impedance becomes negative. Unfortunately, such characteristics have only been utilized to provide, for example, astable multivibrators, switching circuits, etc. Such teachings, coupled with Kobbe, if carried further, could be used to make a circuit for terminating electrical signal transmission lines, for providing a variable aperture correction circuit which provides the special transient effects to correct the distorted television signal uniformly over the dynamic range of the variable control, etc.